1. Field of the Invention
The present invention relates to an AC switch capable of conducting/interrupting a bidirectional current.
2. Description of Related Art
A hybrid vehicle or an electric vehicle includes an electric motor driven by power supplied from a battery as a driving source. More specifically, a capacitor and an inverter are parallelly connected to a main battery, and the electric motor is driven by power supplied from the inverter. When the vehicle decelerates, a regenerative current generated by the electric motor charges the main battery through the inverter. A relay unit is connected between the main battery and the capacitor and the inverter.
A first function required to the relay unit is that of switching on/off a current supplied from the main battery to the electric motor. A second function required to the relay unit is that of switching on/off the regenerative current (a current in the reverse direction) supplied from the electric motor to the main battery. In other words, the relay unit must be capable of switching on/off a bidirectional current. Further, the relay unit must be capable of ensuring insulating properties with a direct current of 400 V when it is in the off state, and capable of continuous conduction of 60 amperes when it is in the on state, for example.
According to a typical prior art, the relay unit is formed by combining mechanical contact relays. More specifically, the relay unit includes a plus-side main relay connected to the positive pole of the main battery and a minus-side main relay connected to the negative pole of the main battery. A series circuit of a precharging relay and a current limiting resistor is parallelly connected to the plus-side main relay. All of the relays are mechanical contact relays. The precharging relay conducts in advance to the plus-side main relay when the key is put in the ignition, to precharge the capacitor with a current limited by the current limiting resistor. Thus, a rush current following subsequent conduction of the plus-side main relay is suppressed.